Colonel Tahir Mahmood, a Sindh Rangers military official, told local media that his group carried out the “information-based operation,” and that 15 suspected criminals were arrested.

A paramilitary force raided the Karachi headquarters of the Muttahida Qaumi Movement (MQM), one of Pakistan's major political parties, in the early hours of Wednesday morning, seizing what they are referring to as "illegal weapons" and detaining several party members. One person reportedly died in the raid.

Colonel Tahir Mahmood, a military official with the Sindh Rangers, which is under the control of the Ministry of the Interior of the Pakistan Government, told local media that his group carried out the "information-based operation," and that 15 suspected criminals were arrested — including Faisal Mota, a central member of the party who was sentenced to death in absentia for the murder of a television journalist in 2011.

An illegal weapons cache containing Kalashnikovs and shotguns was also recovered. It was claimed that some of the weapons had come from a missing NATO container.

The MQM, which has called for a peaceful protest in response to the raid, has confirmed that several party workers were arrested. The group denied that the weapons were kept illegally.

"The weapons present inside the party headquarters are all licensed, and are for security purposes after the party had received threats from the Taliban Pakistan [TTP]," Senator Babar Ghauri of MQM told VICE News.

In November 2012, the Taliban claimed responsibility for an attack on MQM's camp in Orangi Town in the Sindh province, in which one person was killed and 20 were injured.

Schools, shops, and businesses closed today in fear that the raid would provoke a violent reaction across Karachi, as well as in other cities in the Sindh province, including Hyderabad and Sukkur.

Wasay Jalil, an MQM spokesperson, told VICE News that a senior party worker was killed by the security forces, but that the Rangers denied that they shot the worker.

"Dozens of mobiles of Rangers appeared at Nine Zero [the name of the Karachi headquarters] around 6am. Personnel proceeded to raid the 50 offices in our headquarters. They went to each office, went through all the files, and broke telephones," Jali said.

Businesses in parts of Karachi shut their doors on Wednesday, March 11, after a raid on the headquarters of the secular MQM political party.

Altaf Hussain, the leader of the MQM, who has lived in self-imposed exile in London since 1992, asked for calm.

"I believe that time will show this to be a wholly unjustified abuse of power on the part of the establishment," he said.

In June 2014, Hussain was released on bail in London after being arrested on suspicion of money laundering. His arrest sparked major protests in Karachi.

The MQM, formed in the 1980s, traditionally represents the descendants of Urdu-speakers who migrated from India when Pakistan was established in 1947. The party now holds 23 seats in the National Assembly of Pakistan. The party has been accused of political violence, and "was widely viewed as the major perpetrator of targeted killings," according to a 2012 Human Rights Watch report.

After the raid, Hussain broadcast a message to his supporters in the city, saying: "The weapon seized from Nine Zero by Rangers do not belong to MQM."

"If the weapons belonged to MQM, they would not have been stored in Nine Zero. Those recovered were planted by Rangers personnel themselves, who carried it inside, concealed in blankets," he added.

On Twitter, Shireen Mazari of the Pakistan Tehreek-e-Insaf [PTI] called for action from the UK.

About time UK govt took notice of what UK citizen AH keeps in his "house" in Pak. Such an arms cache surely punishable under UK law also?

Hussain recently apologized to Mazari and the PTI's band of female workers for controversial comments, accusing Mazari as "running a brothel" at the party's Azadi March.

In February, Imran Khan, the leader of PTI, branded Hussain as the "biggest terrorist" in Pakistan. Khan made the comments at an event welcoming former Punjab governor Chaudary Sarwar to the PTI. Khan also addressed the Pakistani prime minister, saying "when you met David Cameron, did you not have the courage to tell him that a terrorist killing Pakistanis was living in London?"

Tensions between the PTI and the MQM intensified when a report submitted to the Sindh High Court in February investigating the September 2012 Baldia factory fire, which killed over 250 men and women, accused the MQM as being involved in the incident. The report reveals that a "well-known party high official" had demanded Rs200 million [approximately $2 million] as Bhatta, or extortion money, through a frontman from Ali Enterprises, the owners of the factory, in August 2012.

Khan called attention to the report in Twitter in February.

JIT Report: Shocking to see such inhuman callousness by extortionist mafia which set fire to Baldia Town factory killing over 258 workers.